Howdy:

20gal tank, I add 1/2 TBSP of Barr's GH booster at each water change. My tap has very low GH. After adding 1/2 TBSP GH booster the GH = 60 ppm.

If I want to cover all the bases for a balanced regime, should I also be adding Mg?

I have done searchers here but can not find recommended ppms and quite frankly I don't know how to assess whether this is needed or not and under what circumstances. Dose with macros, with micros, only 1x per week, etc.?

Plant growth is lackluster but there is little algae. Non-co2, Excel, AS substrate, 2wpg, photoperiod about 8hrs. I dose reduced levels of EI.

No, no need for Mg.

Regards,
Tom Barr

Add when ever you do a water change(1-4x a month). If the tank is denser and growing well, you might need a bit more if you do only the rare water change, 1/2 teaspoon once every 1-2 weeks is good.

Regards,
Tom Barr